# Where the lognormal formula comes from

A Quant Finance extension after The lognormal world and before Black–Scholes. Follow Zon and Coach from the normal log-price bell to the dollar-price density, one small step at a time.

Compare two rulers, check matching probability areas, explore the 1/s conversion and distinguish mode, median and mean. Formula meanings, symbol definitions and a collapsed written guide support the interactive.

This premium lesson uses the existing request-access flow. Reset defaults use a $90 stock price, 20% volatility, one year and zero drift.

Canonical page: https://21ifm.com/quant/lognormal-formula

## Explore

- [Quant Finance learning path](https://21ifm.com/quant)
- [Start with The lognormal world](https://21ifm.com/quant/lognormal-world)
- [Apply it in Integrals and expected payoff](https://21ifm.com/basics/integrals)
- [Continue to Black–Scholes](https://21ifm.com/quant/binomial-black-scholes)